Operation

Figure 28 External maintenance bypass switch, single-input UPS

S1-B

UPS Input

Critical load

 

S1-A

S1-C

IMBS

SBS

Rect INV

Battery

The table below summarizes the External Maintenance Bypass switch positions and actions.

Table 3

External maintenance bypass switch positions and actions

 

 

 

 

 

 

Switch position

S1-A

S1-B

S1-C

AUX

 

 

 

 

 

Maintenance (Service)

Open

Closed

Open

Open

 

 

 

 

 

Test (Bypass)

Closed

Closed

Open

Open

 

 

 

 

 

On Line (Transition)

Closed

Closed

Closed

Open

 

 

 

 

 

On Line (Normal)

Closed

Open

Closed

Closed

 

 

 

 

 

 

When the External Maintenance Bypass switch is in Bypass or Maintenance position, the UPSC will assert the bypass contactor close signal and the output contactor open signal. It will also turn on the SBS. Automatic Retransfer operations will be disabled.

If the External Maintenance Bypass switch rotates from the Bypass or Maintenance to the Normal position, then the UPSC will keep the bypass in the ON state, thus keeping the critical bus powered via the bypass source. The user will be able to issue a “Manual Transfer to Inverter” command pro- vided the retransfer conditions are satisfied. The user can also issue a shutdown or a start command.

If the External Maintenance Bypass switch rotates from the Normal to the Bypass or Maintenance position, the UPSC will assert the bypass contactor close signal and the output contactor open signal. It will also turn on the SBS. Automatic Retransfer operations will be disabled.

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Liebert 30-130kVA manual External maintenance bypass switch, single-input UPS